1. Field of the Invention
The present invention relates to Internet messaging. More particularly, the present invention relates to systems, methods, and computer program products for resolving addressing in networks that include a network address translator.
2. Discussion of the Background
The transmission control protocol/Internet protocol (TCP/IP) suite includes four layers, a link layer, a network layer, a transport layer, and an application layer. A detailed explanation of the TCP/IP protocol suite is provided in Stevens, W., “TCP/IP Illustrated, Vol. 1, The Protocols,” Addison-Wesley Publishing Co., 15th printing, October 1999, ISBN: 0-201-63346-9, and Loshin, P., “TCP/IP Clearly Explained,” Morgan-Kaufmann, 3rd Ed., 1999, ISBN: 0-12455826-7, the entire contents of both of which are incorporated herein by reference.
The IP protocol is a network layer protocol for providing an unreliable, connectionless datagram delivery service. TCP and the user datagram protocol (UDP) are transport layer protocols for providing a flow of data between two hosts in a TCP/IP network. TCP provides a reliable connection-based flow of data between two hosts, while UDP provides a simpler, less reliable flow of data between two hosts.
TCP/IP is a packet-based protocol in which packets of information are transported from node to node. Accordingly, each node in a TCP/IP network must have an address that is unique within that network in order to receive those packets that are sent to that node. The TCP, UDP, and IP protocols all include adding header information to packets of information. These headers include the address information of both the source node sending the packet, and the destination node which is the intended recipient of the packet. The IP header includes the source and destination IP addresses, while the UDP header or TCP header include the source and destination port numbers through which the packets are to be communicated.
IP addresses are 32 bits. IP addresses are normally represented in “dotted decimal” format. For example, IP network addresses may be represented as including the range of addresses from 0.0.0.0 to 255.255.255.255.
The Internet is a TCP/IP-based network that includes many other TCP/IP networks. An overview of the Internet is provided in Gralla, P., “How the Internet Works,” Que, Millennium Ed., August 1999, ISBN: 0-7897-2132-5, the entire contents of which is incorporated herein by reference. The phenomenal growth of the Internet has given rise to a concern within the Internet community that the current TCP/IP protocol suite will be unable to accommodate the number of nodes on the Internet. In other words, the 32-bit IP address provided in the TCP/IP protocol may be insufficient. As a short-term solution, the idea of a network address translator (NAT) has been developed by the Internet engineering taskforce (IETF). The IP NAT is described in RFC 1631, available through the IETF website (www.ietf.org). The entire contents RFC 1631 is herein by reference. As described in RFC 1631, the IP NAT is placed at a border between the Internet and another network. By using a NAT, an entire network can share, for example, a single Internet address, through which all external communications will be routed. The NAT simply maintains a translation table that translates packets of information between the individual nodes of the local network, and the common Internet address of the network. By using a NAT, a single Internet address may be shared by an entire network, thereby minimizing the address depletion problem confronting the Internet.
One recognized limitation of a NAT is that the source address included in the IP header of all packets originating from the NAT, and by extension, any of the nodes of the network behind the NAT, is the same. This limitation will impact those applications that rely on knowing their unique Internet address. While each node of the network behind the NAT has a unique IP address for that network, that IP address is not necessarily a globally-unique Internet IP address. Only the IP address of the NAT is guaranteed to be a globally unique IP address.